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{{for|electronic filter circuits rather than synthesizer filters|Filter}}
An audio filter is a frequency dependent amplifier circuit, working in the audio frequency range, 0 Hz to beyond 20 kHz. Audio filters can amplify (boost), pass or attenuate (cut) some frequency ranges.
The '''voltage-controlled filter''' '''(VCF)''' is an [[filter|electronic filter]] whose operating characteristic can be accurately [[CV/gate|voltage controlled]] over a wide audio range.<ref>''[https://books.google.co.uk/books?id=3hjvWzkMK-sC&pg=PA27#v=onepage&q=filter&f=false Analog Days: The Invention and Impact of the Moog Synthesizer]'' by Trevor Pinch and Frank Trocco, Harvard University Press, 2004, {{ISBN|0674016173}}</ref><ref>[https://web.archive.org/web/20191104124000/https://synth-diy.org/pipermail/synth-diy/2019-August/171532.html Article "Analyzing the Moog Filter"] reply by Donald Tillman, Synth-diy mailing list, 23 August 2019</ref>


Common filter types used in audio synthesis include:
Common filter types used in audio synthesis include:
* Low-pass (high-cut) filter - removes higher frequencies

* Low-pass (high-cut) filter: removes higher frequencies
* High-pass (low-cut) filter - removes lower frequencies
* High-pass (low-cut) filter: removes lower frequencies
* Band-pass filter - removes frequencies outside a given band
* Band-pass filter: removes frequencies outside a given band
* Notch filter - removes frequencies within a given band
* Notch filter: removes frequencies within a given band
* Shelf filters - raise or lower frequencies above or below a cut off point.
* Shelf filters: raise or lower frequencies above or below a cut off point.
* Peak filters - raise frequencies within a given band
⚫
* Formant filters - raise multiple peaks, often in such a way that they mimic the human voice.
* Peak filters: Raise frequencies within a given band
* State variable filters - e.g. include simultaneous low-pass, high-pass and band pass outputs as well as voltage controllable cut off frequency and resonance (Q)
⚫
* Formant filters: raise multiple peaks, often in such a way that they mimic the human voice.
* Comb filter - adding a delayed version of a signal to itself, causing constructive and destructive interference.

There are many ways to implement most filters, and each has its own specific audio characteristics or flavour. Some common features across most filter types include:
There are many ways to implement most filters, and each has its own specific audio characteristics or flavour. Some common features across most filter types include:
⚫
* A cut-off frequency - the frequency at which the filter begins to remove frequencies. This is often voltage-controllable and can changes over time (e.g. controlled by an [[Envelope generator|envelope]], or an [[Low frequency oscillator|LFO]]).
⚫
* Resonance - how much the filter boosts the frequency at the cut-off point. This may also be voltage-controllable.
⚫
* Phase shift - frequencies beyond the cut-off often have their [[phase]] affected.


== References ==
⚫
* A cut-off frequency - the frequency at which the filter begins to remove frequencies. This is often [[voltage control|voltage-controllable]], and can changes over time (e.g. controlled by an [[Envelope generator|envelope]], or an [[Low frequency oscillator|LFO]]).
{{reflist}}
⚫
* resonance - how much the filter boosts the frequency at the cut-off point. This may also be voltage-controllable.
⚫
* frequencies beyond the cut-off often have their [[phase]] affected.


[[Category:Synthesizer components]]
[[Category:Synthesizer components]]

Latest revision as of 15:32, 2 July 2023

For electronic filter circuits rather than synthesizer filters, see Filter.

The voltage-controlled filter (VCF) is an electronic filter whose operating characteristic can be accurately voltage controlled over a wide audio range.[1][2]

Common filter types used in audio synthesis include:

  • Low-pass (high-cut) filter - removes higher frequencies
  • High-pass (low-cut) filter - removes lower frequencies
  • Band-pass filter - removes frequencies outside a given band
  • Notch filter - removes frequencies within a given band
  • Shelf filters - raise or lower frequencies above or below a cut off point.
  • Peak filters - raise frequencies within a given band
  • Formant filters - raise multiple peaks, often in such a way that they mimic the human voice.
  • State variable filters - e.g. include simultaneous low-pass, high-pass and band pass outputs as well as voltage controllable cut off frequency and resonance (Q)
  • Comb filter - adding a delayed version of a signal to itself, causing constructive and destructive interference.

There are many ways to implement most filters, and each has its own specific audio characteristics or flavour. Some common features across most filter types include:

  • A cut-off frequency - the frequency at which the filter begins to remove frequencies. This is often voltage-controllable and can changes over time (e.g. controlled by an envelope, or an LFO).
  • Resonance - how much the filter boosts the frequency at the cut-off point. This may also be voltage-controllable.
  • Phase shift - frequencies beyond the cut-off often have their phase affected.

References

  1. ^ Analog Days: The Invention and Impact of the Moog Synthesizer by Trevor Pinch and Frank Trocco, Harvard University Press, 2004, ISBN 0674016173
  2. ^ Article "Analyzing the Moog Filter" reply by Donald Tillman, Synth-diy mailing list, 23 August 2019
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